A typical steering system for an automotive vehicle comprises a rack and pinion mechanism. The rack is operatively connected to wheels of the vehicle and includes teeth. The pinion, also referred to as the drive pinion, engages the rack teeth and is operatively coupled to the steering wheel. A yoke assembly is disposed opposite the pinion to bias the rack against the pinion and prevent slippage. During operation, an operator inputs a steering command by turning the steering wheel to rotate the pinion, which in turn laterally displaces the rack to change the orientation of the wheels.
To reduce the steering force needed by the operator to turn the steering wheel, the vehicle may be equipped with an electric power assist steering system, referred to as EPAS. A conventional EPAS system comprises a second pinion that engages a separate section of the rack and is driven by an electric motor. In response to a steering command from the operator, the motor is actuated to rotate the pinion and thereby reduce the force required to displace the rack.
The drive pinion and yoke are contained within a housing that is a die casting. The die casting includes a bore for the drive pinion, a bore for the section of the rack and a bore for the yoke. These bores are arranged in different angles. During die casting, the bores are formed by cores that are connected to mechanisms that retract the cores to allow the casting to be released from the mold. The assist pinion, which also requires a housing, is located at a separate section of the rack, spaced apart from the drive pinion, and is oriented in still a different direction than the drive pinion. Extension of the rack coring, and the additional slide coring for the assist pinion, add substantially to the complexity and cost of the die casting, making a singular die cast housing prohibitively expensive. Thus, dual pinion steering mechanisms for EPAS systems use separate housings for the drive pinion and the assist pinion, which adds to the number of components and complexity of the manufacturing operations.
Therefore, a need exists for a housing that includes sections for containing a rack, a pinion and a yoke, and that may be readily manufactured without the complexity and cost of slide coring such as needed for die casting.
In addition, a need exists for a dual pinion steering mechanism that includes an integral housing that is readily manufactured as a single component, which housing includes an elongated rack section and separate drive pinion and assist pinion sections that may be independently oriented as desired to optimize the mechanism as needed to meet onboard spatial constraints.